1. Field of the Invention
The present invention is directed to a system and method for locating a device in a closed system hidden from visual observation by a boundary, and in particular, the invention is directed to a system and method for locating a medical device implanted in a human body.
2. Description of Related Art
In a closed system an electronic device is often implanted, disposed or positioned on one side relative to a boundary that prohibits the internal device from being visually observed. Over the course of time removal, maintenance or replacement of the internal device may be required for any number of reasons such as malfunction or depletion of its internal power source having a finite lifespan. In the medical application, implantable devices such as drug infusion pumps, sensors and stimulators, just to name a few, are gaining widespread use in treating a wide variety of medical conditions. Manufactures generally recommend that these implantable medical devices be mounted or sutured via one or more loops disposed along the exterior of the device so as to remain anchored in a substantially fixed location. It is not uncommon, however, for the surgeon to fail to suture the device in place during surgery or for the sutures to disengage permitting the implantable device to migrate through the body to a new location. Clearly determining the exact location of the device must be ascertained prior to or during surgery for its removal.
Even if removal is not necessary, locating the implantable medical device may be necessary to perform some type of maintenance on the device, for example, to replenish fluid (e.g., a drug reservoir) or drain fluid (e.g., drainage pump) therein. Drug infusion pumps are commonly implanted to dispense a medication, such as insulin or pain medication, from an internal supply reservoir via a catheter into the body. Once depleted of fluid, the reservoir must be refilled externally via insertion of a percutaneous needle through a septum covering a refill port. Several pumps feature a supplemental, auxiliary or second bolus port covered by a septum for receiving a bolus injection. A single dosage of fluid is dispensed via bolus injection into the bolus port versus a continuous infusion of medication stored in and dispensed from the internal supply reservoir via a catheter. The quantity or dosage of medication for replenishing the internal supply reservoir is typically greater than that dispensed by way of one time bolus injection. Accordingly, it is important to ensure selection of the correct injection site (e.g., refill port vs. bolus port) so that the patient is not inadvertently bolused with a reservoir refill volume of mediation. An overdose in medication via the inadvertent or accidental delivery of the refill supply reservoir quantity of fluid in a single dosage via the bolus port could result in adverse consequences, perhaps even death, to the patient.
Heretofore, locating the implantable drug infusion pump itself within the body has been realized through physical palpitation or manipulation. Once the position of the pump itself has been ascertained, it may be necessary to find the pump refill port or bolus port for injecting medication therein. The pump device is generally designed so that the refill and bolus ports are raised relative to the housing and thus susceptible to being identified by further physical palpitation or manipulation. However, as described above, it is imperative to the health of the patient that the pump refill port and bolus port be readily distinguished from one another prior to injection of the medication into the pump. For obvious reasons, the use of physical palpitation or manipulation alone to locate the raised port of interest is imprecise and subject to human error. Alternatively, or in combination with physical palpitation or manipulation, a pump specific template, typically provided by the manufacturer, may be positioned over the device, once it has been located, to precisely identify the intended port.
Such conventional methods and techniques are disadvantageous under certain circumstances. If the implantable device has dislodged from its original position and migrated through the body it may be difficult and time consuming to locate using only physical manipulation or palpitation. Especially in patients that are obese, physical palpitation and/or the use of templates are often impractical techniques for locating the device itself, much less the appropriate port.
A more sophisticated and precise approach as described in U.S. Pat. Nos. 6,305,381 and 6,009,878 employs an emitter on the implant side. An implant coil 22 is disposed around or beneath a septum 24. Instructions are received telemetrically by the implant to activate the implant coil 22. Energy is emitted from the coil and radiates therefrom. An implant location antenna array 103 including three antennas is moved externally along the patient's surface. Energy received by the implant location antenna array is detected by each of three antennas. It is presumed that the antennas are an equal distance away from the implant coil 22 and thus aligned with the septum when each of the antennas in the array are sensing the same amount of energy. This technique is problematic in that the emitter on the implant side consumes energy from the limited internal power source associated with the implantable medical device thereby shortening its lifespan.
U.S. Pat. No. 5,375,596 discloses an alternative method and apparatus for determining the position of catheters, tubes, placement guidewires and implantable ports within biological tissue. An external transmitter/detector unit 2 is positioned proximate the patient's skin and an antenna 14 emits an RF signal wherein the magnetic flux lines 36 project radially into the patient's body. The emitted RF field 36 is detected by an antenna of a device such as a catheter 30, 72 implanted internal to the body that is electrically connected to the external transmitter/detector unit 2 via a cable 16 and clip 18. In a particular application of the patented invention, a port access needle or infusion needle assembly 84 is employed to refill a reservoir of an implanted port assembly 64 with fluid to be dispensed through the body via a catheter 72. At the bottom of the internal cavity of the port body is a layer of conductive mesh 80 covered by a sealant layer 78. To determine the positioning of the catheter 72 an electrical connection must first be established between the external transmitter/detector unit 2 and the implanted port assembly 64. This is achieved by passing the needle through the sealant layer 78 so that it terminates with the conductive mesh 80 of the port body of the implant in order to complete the electrical connection. Requiring proper insertion of the needle into the port assembly as a preliminary step prior to locating the port itself defeats the underlying purpose of the present invention.
Moreover, this patented locating technique requires the use of a specialized or specific needle having a conductor exposed at each end. As disclosed in the patent, the conductive element disposed at the proximal end is adapted to be electrically coupled via a cable to the transmitter/detector 2 of the external device, while the exposed terminal end of the conductive element completes the electrical connection when properly inserted into the conductive mesh 80. Once the electrical connection has been completed (i.e., the exposed terminal end of the conductive element of the needle is properly inserted into the port so that it contacts the conductive mesh), antenna 14 of transmitter/detector 2 is passed over the surface of the patient's skin and RF field 36 radiates into the tissue of the patient. As that radiation is received by the antennas 32 in the catheter tube 34 a signal is conducted to the detector circuitry within transmitter/detector 2 by clip 18 and cable 16. By monitoring the signal from the catheter antenna 32, the location of the catheter may be determined. The physical wiring or cable link between the external transmitter/detector unit 2 and the internal device is also problematic in that there is always a high degree of risk of infection at the point of entry/exit through the skin.
It is therefore desirable to develop an improved system and method for locating a device disposed on one side of a closed system that solves the aforementioned problems associated with conventional devices.